Neither. I'm saying that common for two parties to sign a contract that agrees a payment schedule based on delivery milestones, and for one party to withhold payment because they think the other party hasn't delivered what they said they would deliver. For example, if X commissions a website from Y that says X will pay when the website is "done", X will refuse to pay Y until X thinks it's fast enough, or has a feature that Y didn't think they would have to develop, etc. The negotiation is around whether or not the terms of the contract have been fulfilled.

If you've signed up for a payment plan for £xx/month and overnight it goes up to £xx+30%/month in August, with the threat of another similar price hike in January, it could be argued that the energy companies broke the contract.

Yes, there has always been the possibility of prices rising. But there's also always been a reasonable expectation that any price rises would be in line with inflation. Not +30% twice in the space of a few months.